JP2018030100A - Catalyst for exhaust purification, and method for producing the same, and catalyst converter for exhaust purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for exhaust purification that has excellent heat resistance and also has excellent catalyst performance even after exposure to high temperature, and a method for producing the same, and a catalyst converter for exhaust purification.SOLUTION: A catalyst for exhaust purification 100 at least contains a base particle 11 containing zirconia oxide, and an LaFeOfine particle 21 and an iron oxide fine particle 31 carried together on a surface 11a of the base particle 11.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification catalyst in which LaFeO ₃ and iron oxide are co-supported on base material particles, a method for producing the same, and an exhaust gas purification catalyst converter.

  Platinum group elements such as platinum, palladium, rhodium, iridium, ruthenium, and osmium in the purification of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines such as automobiles A three-way catalyst (TWC) using PGM (Platinum Group Metal) as a catalytically active component is widely used. However, PGM is relatively expensive and there are concerns about securing a stable supply over the medium to long term. Therefore, development of a new catalyst material that does not require PGM is being studied.

  For example, Patent Document 1 (Japanese Patent Laid-Open No. 2005-125317) discloses a carrier containing a ceria-zirconia solid solution having a specific pore diameter and pore volume, and iron oxide as an active species mixed or supported on the carrier. And an oxygen storage / release material characterized by comprising:

Patent Document 2 (Japanese Patent Laid-Open No. 10-216509) discloses a cerium-based composite oxide of Y solid solution ceria-zirconia Ce _0.6 Zr _0.30 Y _0.10 O _1.95 and Fe supported on the cerium-based composite oxide. An oxygen storage cerium-based composite oxide is disclosed.

On the other hand, Patent Document 3 (Japanese Patent Application Laid-Open No. 2010-069451) discloses spherical particles made of an oxide fired body having a perovskite structure, the average particle diameter of which is in the range of 10 to 50 μm, and the specific surface area. perovskite oxide catalyst lies in the range of 10m ² / g~40m ² / g are disclosed.

Furthermore, exhaust gas purification catalysts in which alkaline earth metal oxides or alkali metals are used in combination with perovskite complex oxides have been studied.
For example, Patent Document 4 (JP 2010-194487), a defect perovskite-type composite oxide _{(BaY 2-x Sc x O} 4 or _{BaY 2-x In x O 4} ) and alkaline earth metal oxides ( NOO purification catalyst is disclosed in which, in powder X-ray diffraction, substantially only the diffraction pattern of the defect perovskite complex oxide is detected in powder X-ray diffraction.

JP 2005-125317 A Japanese Patent Laid-Open No. 10-216509 JP 2010-069451 A JP 2010-194487 A

  In recent years, in exhaust gas purification of internal combustion engines, further improvement in catalyst purification performance has been demanded as global exhaust gas regulations are strengthened. Direct catalytic converter is installed directly under the exhaust manifold where the exhaust gas temperature is high to improve the purification performance during the so-called cold start immediately after engine startup or to improve the purification performance when used in cold regions. Adoption of catalytic converters is progressing. In connection with this, the exhaust gas purification catalyst has been required to further improve heat resistance.

Furthermore, with the advancement of air-fuel ratio (A / F) control to cope with exhaust gas regulations and fuel efficiency improvements, lean environment (oxidizing atmosphere), stoichiometric environment (theoretical air-fuel ratio), and rich environment (reducing atmosphere) ) Switching of the processing atmosphere has become precise. Here, in the catalyst system of Patent Document 1, iron (Fe) is reduced and produced from iron oxide (Fe ₂ O ₃ ) in a rich environment, and this functions as a highly active active species. However, in actuality, when the catalyst system of Patent Document 1 is exposed to a high temperature environment, the particles on the support are sintered together to grow and the number of catalytically active sites (active species particles on the support) is remarkably reduced. Therefore, there has been a problem that the catalyst performance is greatly deteriorated after high temperature exposure. That is, the oxygen storage / release material of Patent Document 1 has a large difference between the performance immediately after synthesis (initial performance) and the performance after high temperature exposure (running performance), and the number of catalytically active sites after high temperature exposure is small. Therefore, there is a lot of room for improvement, and it was poor in practicality as an exhaust gas purification catalyst for use in a high temperature environment. These problems also apply to the catalyst system of Patent Document 2.

On the other hand, the perovskite type oxidation catalyst has a problem that it has a small surface area and it is difficult to obtain a desired activity. In order to solve this, in the catalyst system of Patent Document 3, the CaMnO ₃ catalyst is granulated to the order of several tens of μm, and the oxidation catalyst performance of propylene is enhanced by securing a predetermined specific surface area. However, the catalyst system of Patent Document 3 still has insufficient catalytic activity sites, and when it is used as an exhaust gas purification catalyst that is exposed to a high temperature environment, it maintains its specific surface area even after high temperature exposure. However, it was not practical as an exhaust gas purifying catalyst for use in a high temperature environment.

  In the catalyst system of Patent Document 4, the catalytic activity, particularly the low temperature activity is improved by using an alkaline earth metal oxide or an alkali metal in combination, but these have insufficient heat resistance, and in a high temperature environment. It was poor in practicality as an exhaust gas purification catalyst to be used.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an exhaust gas purifying catalyst, a manufacturing method thereof, an exhaust gas purifying catalytic converter, and the like that have not only excellent heat resistance but also excellent catalytic performance even after high temperature exposure. There is.

The present inventors diligently studied to solve the above problems. As a result, the present inventors have found that the above problems can be solved by adopting a new structure in which LaFeO ₃ fine particles and iron oxide fine particles are adhered in a highly dispersed manner on predetermined base material particles, and the present invention has been completed.

That is, the present invention provides various specific modes shown below.
(1) For exhaust gas purification, comprising at least base material particles containing zirconia-based oxide and LaFeO ₃ fine particles and iron oxide fine particles co-supported on the surface of the base material particles catalyst.
(2) The content ratio of La and Fe is a molar ratio, and the following formula (1):
0.6 <Fe / La ≦ 1.6 (1)
The exhaust gas purifying catalyst according to (1), wherein the exhaust gas purifying catalyst is satisfied.

(3) The exhaust gas purification catalyst according to (1) or (2), wherein the LaFeO ₃ fine particles have an average crystallite diameter of 1 to 50 nm.
(4) The exhaust gas purifying catalyst according to any one of (1) to (3), wherein the zirconia-based oxide is a rare earth element solid solution zirconia.
(5) the base material particles, the has an average particle diameter _{D 50} of 3 to 30 .mu.m (1) ~ (4) or the exhaust gas purifying catalyst according to one of.
(6) At least a catalyst carrier and the exhaust gas purifying catalyst according to any one of the above (1) to (5) held on at least a part of the catalyst carrier are provided. And catalytic converter for exhaust gas purification.

(7) Applying an aqueous solution containing at least La ions and Fe ions to the surface of the base material particles containing the zirconia-based oxide, and heat-treating the base material particles after the treatment at 500 to 1490 ° C. And a step of co-supporting LaFeO ₃ fine particles and iron oxide fine particles on the surface of the base material particles, and a method for producing an exhaust gas purifying catalyst.
(8) The content ratio of La and Fe in the aqueous solution is a molar ratio represented by the following formula (1):
0.6 <Fe / La ≦ 1.6 (1)
The method for producing an exhaust gas purifying catalyst according to (7), wherein

(9) The method for producing an exhaust gas purifying catalyst according to (7) or (8), wherein the LaFeO ₃ fine particles have an average crystallite diameter of 1 to 50 nm.
(10) The method for producing an exhaust gas purification catalyst according to any one of (7) to (9), wherein the zirconia-based oxide is a rare earth element solid solution zirconia.
(11) the base material particles (7) having an average particle diameter _{D 50} of 3 to 30 .mu.m ~ (10) any method of manufacturing the exhaust gas purifying catalyst according to one of.

According to the present invention, it is possible to realize an exhaust gas purifying catalyst, a manufacturing method thereof, an exhaust gas purifying catalytic converter, and the like that have excellent heat resistance and excellent catalytic performance even after high temperature exposure. . The exhaust gas purifying catalyst of the present invention is a catalyst particle having a composite structure in which a large number of minute active sites (LaFeO ₃ fine particles and iron oxide fine particles) are supported on base material particles. Based on the composition and structure of the catalyst particles, It can be particularly suitably used as a three-way catalyst (TWC: Tree Way Catalyst) that reduces NOx, CO, HC, etc. in the exhaust gas. In addition, the exhaust gas purifying catalyst of the present invention does not use a platinum group element (PGM) or a noble metal element (PM) as an essential component, and thus is excellent in economic efficiency. Moreover, unlike conventional catalysts using inferior heat resistance such as zeolite, the exhaust gas purifying catalyst of the present invention can be mounted on an engine direct type catalytic converter, an tandem direct type catalytic converter, etc. Therefore, the canning cost can be reduced.

1 is a schematic diagram showing a schematic configuration of an exhaust gas purifying catalyst 100 according to an embodiment. It is a graph and model gas composition which show the measurement conditions of NO purification rate in a test example. It is a graph which shows the measurement result of NO purification rate of a test example. 2 is an X-ray diffraction pattern of the exhaust gas purifying catalyst of Example 1. FIG. FIG. 5 shows the EPMA elemental analysis results of the exhaust gas purification catalyst of Example 3 and the EPMA elemental analysis results of the exhaust gas purification catalyst of Comparative Example 1. FIG. It is an EPMA elemental analysis result of the exhaust gas purifying catalyst of Example 5 and Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to these. In this specification, for example, the description of a numerical range of “1 to 100” includes both the upper limit value “1” and the lower limit value “100”. This also applies to other numerical range notations.

FIG. 1 is a schematic diagram showing a schematic configuration of an exhaust gas purifying catalyst 100 according to an embodiment of the present invention. The exhaust gas purifying catalyst 100 contains at least base material particles 11 containing a zirconia-based oxide, LaFeO ₃ fine particles 21 and iron oxide fine particles 31 co-supported on the surface 11a of the base material particles 11. It is characterized by that. Hereinafter, each component will be described in detail.

  Examples of the zirconia-based oxide contained in the base material particle 11 include zirconia and zirconia composite oxide in which zirconia is doped with other elements. Zirconium is suitable as a base material for an exhaust gas purification catalyst used in a high temperature environment because of its excellent heat resistance. Zirconium has a high oxygen exchange rate at a high temperature of 600 ° C. or higher, and is excellent in responsiveness in switching the exhaust gas treatment atmosphere. Therefore, by using the zirconia-based oxide for the base material particles 11, oxygen absorption / release necessary for the catalytic reaction is performed, the catalytic reaction is promoted, and high NOx purification performance is obtained. Furthermore, in this catalyst system, the use of zirconia-based oxides has an advantage that solid solution of La and Fe to be co-supported is suppressed as compared with alumina. The zirconia-based oxide may contain hafnium (Hf), which is usually contained in the ore in an amount of about 1 to 2% by mass, as an inevitable impurity. The total amount of inevitable impurities excluding hafnium is preferably 0.3% by mass or less. For example, a part of cerium or zirconium may be substituted with an alkali metal element, an alkaline earth metal element, or the like. Moreover, you may contain transition metal elements, such as iron (Fe), cobalt (Co), nickel (Ni), titanium (Ti), and copper (Cu).

Among these, zirconia-based oxides are preferably those in which a rare earth element is further solid-solved, that is, rare earth element solid-solution zirconia. By using a zirconia-based oxide in which a rare earth element is dissolved, lattice oxygen deficiency (δ) can be easily adjusted, and exhaust gas purification performance tends to be improved. Further, the dispersibility of the co-supported LaFeO ₃ fine particles 21 and iron oxide fine particles 31 is enhanced, and further, grain growth due to sintering during high heat exposure tends to be suppressed. Examples of rare earth elements include yttrium, cerium, scandium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these, yttrium (Y), cerium (Ce), La (lanthanum), praseodymium (Pr), and neodymium (Nd) are preferable from the viewpoints of stability of the crystal structure, heat resistance, and the like. In addition, these rare earth metals R can be used individually by 1 type or in combination of 2 or more types as appropriate. These rare earth elements are preferably the total amount of oxides of the above listed rare earth elements in terms of the total amount of zirconia-based oxide (for example, the sum of Y ₂ O ₃ , Nd ₂ O _3, etc.), and is preferably 5 to 45% by mass, More preferably, it is 10-40 mass%.

  Preferred examples of the zirconia-based oxide include perovskite oxides / composite oxides, and include Y—Zr—Ox, Nd—Zr—Ox, La—Zr—Ox, Pr—Zr—Ox, Y—Nd—. Zr-Ox, Y-La-Zr-Ox, Y-Pr-Zr-Ox, Nd-La-Zr-Ox, Nd-Pr-Zr-Ox, La-Pr-Zr-Ox, Y-Nd-La- Zr-Ox, Y-Nd-Pr-Zr-Ox, Y-La-Pr-Zr-Ox, Nd-La-Pr-Zr-Ox, Y-Zr-Ce-Ox, Nd-Zr-Ce-Ox, La-Zr-Ce-Ox, Pr-Zr-Ce-Ox, Y-Nd-Zr-Ce-Ox, Y-La-Zr-Ce-Ox, Y-Pr-Zr-Ce-Ox, Nd-La- Zr-Ce-Ox, Nd-Pr-Zr-Ce-Ox, La-Pr-Zr-Ce Ox, Y-Nd-La-Zr-Ce-Ox, Y-Nd-Pr-Zr-Ce-Ox, Y-La-Pr-Zr-Ce-Ox, Nd-La-Pr-Zr-Ce-Ox, etc. Although rare earth element solid solution zirconia of these is mentioned, It does not specifically limit to these. A zirconia-type oxide can be used individually by 1 type or in combination of 2 or more types as appropriate. In these exemplifications, the display is focused on the combination of the constituent elements contained in each composite oxide, and the stoichiometric ratio of each constituent element is not displayed. That is, the stoichiometric ratio of each constituent element can be arbitrarily adjusted.

Here, from the viewpoint of increasing the amount of LaFeO ₃ and iron oxide supported while maintaining a large specific surface area, and increasing the number of the catalytically active sites by increasing the heat resistance, the base material particle 11 is 3 to 3 preferably has an average particle diameter _{D 50} of 30 [mu] m, more preferably 3 to 15 [mu] m, more preferably from 4 to 10 [mu] m. In the present specification, the average particle diameter D ₅₀ means the median size measured by a laser diffraction type particle size distribution measuring device (for example, manufactured by Shimadzu Corporation, a laser diffraction particle size distribution measuring apparatus SALD-7100 etc.) .

  As the parent particles 11, commercially available products of various grades can be used. In addition, the parent particles 11 made of the zirconia-based oxide having the various compositions described above can also be produced by methods known in the art. Although the manufacturing method of a zirconia-type oxide is not specifically limited, A coprecipitation method and an alkoxide method are preferable.

  As the coprecipitation method, for example, an alkali substance is added to an aqueous solution in which a zirconium salt and a rare earth metal element to be blended as necessary are mixed at a predetermined stoichiometric ratio to cause hydrolysis or coprecipitation of a precursor. A method of baking the hydrolysis product or coprecipitate is preferred. The kind of various salt used here is not specifically limited. In general, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable. Moreover, the kind of alkaline substance is not particularly limited. In general, an aqueous ammonia solution is preferred. As the alkoxide method, for example, a production method in which a mixture obtained by mixing zirconium alkoxide and a rare earth metal element to be blended as necessary at a predetermined stoichiometric ratio is hydrolyzed and then fired is preferable. The kind of alkoxide used here is not particularly limited. In general, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and these ethylene oxide adducts are preferable. Further, the rare earth metal element may be blended as a metal alkoxide or as the various salts described above.

  The firing conditions may be in accordance with conventional methods and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. The firing temperature and treatment time vary depending on the desired composition of the zirconia-based oxide and its stoichiometric ratio, but generally from 150 to 1300 ° C. for 1 to 12 hours from the viewpoint of productivity and the like. More preferably, it is 350 to 800 ° C. for 2 to 4 hours. Prior to the high temperature firing, it is preferable to perform drying under reduced pressure using a vacuum dryer or the like, and to perform a drying treatment at about 50 ° C. to 200 ° C. for about 1 to 48 hours.

This exhaust gas purification catalyst 100 has one characteristic in that it has a composite structure in which LaFeO ₃ fine particles 21 and iron oxide fine particles 31 are co-supported on the surface 11a of the base material particles 11 described above. That is, the exhaust gas purification catalyst 100 has a composite structure in which LaFeO ₃ fine particles 21 and iron oxide fine particles 31 are adhered to the surfaces 11 a of the base material particles 11 in a highly dispersed manner. By adopting such a composite structure, in the exhaust gas purifying catalyst 100, deterioration of the catalyst performance after high temperature exposure is greatly suppressed. The reason is not clear, but the LaFeO ₃ fine particles 21 present on the surface 11a of the base material particle 11 reduce the chance of contact between the iron oxide fine particles 31 on the surface 11a of the base material particle 11, thereby causing high temperature exposure. It is assumed that sintering and grain growth of the iron oxide fine particles 31 are inhibited.

LaFeO ₃ is a perovskite oxide, and exhibits catalytic activity to purify exhaust gas such as NOx based on its own lattice oxygen deficiency. The catalytic action of LaFeO ₃ increases or decreases depending on the amount of lattice oxygen vacancies, but exhibits catalytic activity over the entire range of lean environment, stoichiometric environment, and rich environment. On the other hand, iron oxide takes various oxidation states (for example, Fe ₂ O ₃ , Fe ₃ O ₄ , FeO) according to the external environment. In particular, in the reduced state, it exists in the state of Fe (simple substance), which is a highly active active species, and therefore exhibits a particularly strong catalytic activity in a stoichiometric environment to a rich environment. Therefore, by using LaFeO ₃ together with iron oxide, the catalytic action of exhaust gas purification is reinforced over the entire range of lean environment to stoichiometric environment to rich environment, and platinum group element (PGM) is not used as an essential component. In addition, excellent exhaust gas purification performance is shown.

From the viewpoint of further enhancing the catalytic activity and inhibiting sintering and grain growth of the iron oxide fine particles 31, the LaFeO ₃ fine particles 21 preferably have an average crystallite diameter of 1 to 50 nm, more preferably 3 to 40 nm. It is. For the same reason, the iron oxide fine particles 31 preferably have an average crystallite diameter of 1 to 50 nm, more preferably 3 to 40 nm. By making such fine LaFeO ₃ fine particles 21 and iron oxide fine particles 31 exist on the surface 11a of the base material particle 11, the surface area can be maintained high and a large number of catalytically active sites can be maintained.

The crystallite means the largest group that can generally be regarded as a single crystal, and the size of the crystallite is called the crystallite diameter. Further, in this specification, the average crystallite diameter means a value calculated from a Scherrer equation represented by the following equation (2) based on a measurement result obtained by measuring a diffraction pattern using an X-ray diffractometer. To do.
Crystallite diameter D (Å) = K · λ / (β · cos θ) (2)
In equation (2), K is a Scherrer constant, and here K = 0.9. Also, λ is the wavelength of the X-ray tube used, β is the half width, and θ is the diffraction angle (rad).

Here, the presence ratio (content ratio) of the LaFeO ₃ fine particles 21 and the iron oxide fine particles 31 further increases the catalytic activity and inhibits the sintering and grain growth of the iron oxide fine particles 31, thereby deteriorating the catalyst performance after high temperature exposure. From the viewpoint of suppression, it is preferably in the range of 0.6 <Fe / La ≦ 1.6 in terms of the molar ratio of La and Fe.

The content of the iron oxide fine particles 31 is not particularly limited, but is 0.05 to 10 in terms of Fe ₂ O _{3 with} respect to the total amount of the exhaust gas purifying catalyst 100 from the viewpoint of improving catalyst performance and low-temperature activity. % By mass is preferable, and more preferably 0.1 to 5% by mass.

The content of the LaFeO ₃ fine particles 21 is not particularly limited, but is 0 with respect to the total amount of the exhaust gas purifying catalyst 100 from the viewpoint of improving the catalyst performance over the entire range of lean environment, stoichiometric environment, and rich environment. 0.05 to 10% by mass is preferable, and 0.1 to 5% by mass is more preferable.

The exhaust gas purifying catalyst 100 includes gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), and the like. Even if no precious metal element (PM) or platinum group element (PGM) is used as an essential component, it has excellent heat resistance and excellent catalytic performance even after high temperature exposure. Therefore, it is preferable that the exhaust gas purifying catalyst 100 does not substantially contain a noble metal element (PM) and a platinum group element (PGM) from the viewpoint of economy and stable supply. Here, “substantially not contained” means that the total amount of the noble metal element (PM) and the platinum group element (PGM) is in the range of 0 to 1.0 mass% with respect to the total amount of the exhaust gas purification catalyst 100. More preferably, it is 0-0.5 mass%, More preferably, it is 0-0.3 mass%. Here, when the exhaust gas purifying catalyst 100 contains a noble metal element (PM) or a platinum group element (PGM), these are supported on the surface of the base material particle 11, the LaFeO ₃ fine particle 21 and / or the iron oxide fine particle 31. It only has to be.

The shape of the exhaust gas purification catalyst 100 is not particularly limited. The catalyst powder which is an aggregate of catalyst particles in which LaFeO ₃ fine particles 21 and iron oxide fine particles 31 are co-supported on the base material particles 11 can be used. Further, for example, the catalyst powder can be formed into an arbitrary shape to form a granular or pellet shaped catalyst. Further, the exhaust gas purification catalyst 100 can be supported on a catalyst carrier. As the catalyst carrier used here, those known in the art can be appropriately selected. Representative examples include a ceramic monolith carrier made of cordierite, a metal honeycomb carrier made of stainless steel, a wire mesh carrier made of stainless steel, etc., but are not particularly limited thereto. In addition, these can be used individually by 1 type or in combination of 2 or more types as appropriate.

  The exhaust gas purification catalyst 100 described above is useful, for example, as an exhaust gas purification catalyst for an internal combustion engine, particularly as an exhaust gas purification catalyst for automobiles.

The method for producing the exhaust gas purifying catalyst 100 is not particularly limited as long as a method in which LaFeO ₃ fine particles 21 and iron oxide fine particles 31 are co-supported on the base material particles 11 as described above is obtained. From the viewpoint of producing the exhaust gas purifying catalyst 100 with good reproducibility and at a low cost, an evaporation to dryness method (impregnation method) or the like is preferable.

  As the evaporation to dryness method, a manufacturing method in which the base material particle 11 described above is impregnated with an aqueous solution containing at least lanthanum ions and iron ions and then fired is preferable. By this impregnation treatment, lanthanum ions and iron ions are adsorbed (attached) to the surfaces 11 a of the base material particles 11 in a highly dispersed state. Here, lanthanum ions and iron ions can be blended in the aqueous solution as various salts of lanthanum and iron. The kind of various salt used here is not specifically limited. In general, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable.

The firing conditions may be in accordance with conventional methods and are not particularly limited. The firing atmosphere is preferably an oxidizing atmosphere or an air atmosphere. The firing temperature and treatment time vary depending on the desired composition of the zirconia-based oxide and the stoichiometric ratio, but from the viewpoint of the production and productivity of LaFeO ₃ , it is generally 0 at 500 to 1490 ° C. .1 to 12 hours are preferable, and more preferably 550 to 800 ° C. for 0.5 to 6 hours. Prior to the high temperature firing, drying under reduced pressure may be performed using a vacuum dryer or the like, and a drying treatment may be performed at about 50 ° C. to 200 ° C. for about 1 to 48 hours. By this firing treatment, LaFeO ₃ fine particles and iron oxide fine particles highly dispersed in a nano-order size are generated (synthesized) on the surfaces 11 a of the base material particles 11.

The content ratios of La and Fe in the aqueous solution may be adjusted so that LaFeO ₃ fine particles and iron oxide fine particles have a desired content ratio in the obtained exhaust gas purification catalyst 100. From the viewpoint of suppressing deterioration of catalyst performance due to high temperature exposure, the content ratio of La and Fe in the aqueous solution preferably satisfies the following formula (1) as a molar ratio.
0.6 <Fe / La ≦ 1.6 (1)

  The aqueous solution is made of rare earth elements such as yttrium, cerium, scandium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, lithium, sodium, and potassium. Alkali metal elements such as beryllium, magnesium, calcium, strontium, barium and the like, and transition metal elements such as cobalt, nickel, titanium and copper may be contained. In addition, these can be used individually by 1 type or in combination of 2 or more types as appropriate.

  Here, the exhaust gas purifying catalyst 100 obtained as described above may further carry a noble metal element or a platinum group element as necessary. The method for supporting the noble metal element or the platinum group element is not particularly limited, and a known method can be applied. For example, a solution of a salt containing a noble metal element or a platinum group element is prepared, the exhaust gas purifying catalyst 100 is impregnated with the salt containing solution, and then calcined to carry the noble metal element or the platinum group element. Can do. The salt-containing solution is not particularly limited, but an aqueous nitrate solution, dinitrodiammine nitrate solution, aqueous chloride solution and the like are preferable. Moreover, although a baking process is not specifically limited, About 1 to 12 hours are preferable at 350 to 1000 degreeC. Prior to the high temperature firing, it is preferable to perform drying under reduced pressure using a vacuum dryer or the like, and to perform a drying treatment at about 50 ° C. to 200 ° C. for about 1 to 48 hours.

  The exhaust gas purifying catalyst 100 obtained in this way can be used as the catalyst powder as an aggregate of catalyst particles, but the catalyst powder can be formed into an arbitrary shape to form a granular or pellet shaped catalyst, or a catalyst carrier It is possible to make a monolithic carrier by holding it. It should be noted that various known dispersing devices, kneading devices, and molding devices can be used when producing the molded catalyst. In addition, when the exhaust gas purification catalyst 100 is held on the catalyst carrier, various known coating methods, wash coat methods, and zone coat methods can be applied.

  Hereinafter, the features of the present invention will be described more specifically with reference to test examples, examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

(Test Example 1)
As a base material particle, a zirconia-based oxide (described as Y-ZrO ₂ , Y ₂ O ₃ : 35% by mass, ZrO ₂ : 65% by mass: D ₅₀ = 6.4 μm: BET specific surface area: 72 m ² / g) Using. In this specification, the BET specific surface area refers to a specific surface area / pore distribution measuring device (trade name: BELSORP-mini II, manufactured by Microtrack Bell Co., Ltd.) and analysis software (trade name: BEL_Master, Microtrack Means a value determined by the BET single point method. 1.25 parts by mass of iron nitrate nonahydrate (containing 40% by mass in terms of Fe ₂ O ₃ ) was dissolved in 3.25 parts by mass of water to prepare an Fe-containing aqueous solution. By impregnating the above zirconia-based oxide with an iron-containing aqueous solution and calcining at 600 ° C. for 30 minutes, as an exhaust gas purifying catalyst of Test Example 1, 10 parts by mass of Fe-ZrO ₂ powder catalyst carrying Fe oxide (Fe ₂ O ₃ equivalent loading: 0.5 parts by mass) was obtained.

<Lab measurement of NO purification rate of powder particles>
Using the obtained powder catalyst of Test Example 1, the NO purification rate at the stoichiometric air-fuel ratio at the time of return from the fuel cut (F / C) control was measured. The NO purification rate was measured using a gas analyzer (trade name: BEL Mass, manufactured by Microtrack Bell Co., Ltd.) under the conditions of a measurement temperature of 700 ° C. and a catalyst amount of 50 mg. Further, the F / C control and the model gas composition are as shown in FIG.
The NO purification rate was calculated based on the following formula (3).
NO purification rate (%) = 100− (NO-MASS peak intensity (during measurement) / NO-MASS peak intensity (Blank)) × 100 (3)

(Test Example 2)
As the base material particles, a zirconia-based oxide (described as Nd—ZrO ₂ , Nd ₂ O ₃ : 15 mass%, ZrO ₂ : 85 mass%, D ₅₀ = 5.7 μm, BET specific surface area: 63 m ² / g is used. Except for this, it is carried out in the same manner as in Test Example 1, and as an exhaust gas purification catalyst of Test Example 2, 10 parts by mass of Nd—ZrO ₂ powder catalyst supporting iron oxide (Fe ₂ O ₃ equivalent load: 0.5 mass) Part).

(Comparative Test Example 1)
Exhaust gas purifying catalyst of Comparative Test Example 1 except that alumina (Al ₂ O ₃ , D ₅₀ = 28 μm, BET specific surface area: 141 m ² / g) is used as the base material particle. As a result, 10 parts by mass of an Al ₂ O ₃ powder catalyst supporting iron oxide (Fe ₂ O ₃ equivalent supported amount: 0.5 parts by mass) was obtained.

  The evaluation results are shown in FIG. As is clear from FIG. 3, it was confirmed that Test Examples 1 and 2 were significantly superior in NO purification rate compared to Comparative Test Example 1. From these results, it was shown that zirconia-based oxides are superior to alumina as base material particles for supporting active species.

Example 1
As base material particles, Nd solid solution zirconia oxide (described as Nd—ZrO ₂ , Nd: 15 mass%, ZrO ₂ : 85 mass%, D ₅₀ = 5.7 μm, BET specific surface area: 63 m ² / g). Using. 1.25 parts by mass of iron nitrate nonahydrate (containing 40% by mass in terms of Fe ₂ O ₃ ) and 2.0 parts by mass of lanthanum nitrate hexahydrate (containing 75% by mass in terms of La ₂ O ₃ ) It melt | dissolved in 3.25 mass parts and prepared Fe and La containing aqueous solution. The zirconia-based oxide is impregnated with an Fe- and La-containing aqueous solution, and calcined at 600 ° C. for 30 minutes, whereby 10 parts by mass (Fe ₂ O ₃ ) of Nd—ZrO ₂ powder catalyst in which LaFeO ₃ fine particles and iron oxide fine particles are co-supported. (Conversion carrying amount: 0.5 part by mass).
Thereafter, the obtained powder catalyst was subjected to a high temperature exposure treatment in an endurance furnace to obtain the exhaust gas purifying catalyst of Example 1. As the high temperature exposure treatment, heat treatment was performed at 980 ° C. for 6 hours while sequentially switching the external atmosphere to A / F = 12.5, nitrogen atmosphere, and oxygen atmosphere.

(Example 2)
Except for changing the blending amounts of iron nitrate nonahydrate and lanthanum nitrate hexahydrate to 1.25 parts by mass and 1.35 parts by mass, the same procedure as in Example 1 was carried out to obtain LaFeO ₃ fine particles and iron oxide. 10 parts by mass of Nd—ZrO ₂ powder catalyst in which fine particles were co-supported (Fe ₂ O ₃ equivalent supported amount: 0.5 part by mass) was obtained.
Then, it carried out similarly to Example 1 and the exhaust gas purification catalyst of Example 2 was obtained.

(Example 3)
Except that the blending amounts of iron nitrate nonahydrate and lanthanum nitrate hexahydrate are changed to 1.25 parts by mass and 0.9 parts by mass, the same procedure as in Example 1 was performed, and LaFeO ₃ fine particles and iron oxide were obtained. 10 parts by mass of Nd—ZrO ₂ powder catalyst in which fine particles were co-supported (Fe ₂ O ₃ equivalent supported amount: 0.5 part by mass) was obtained.
Then, it carried out similarly to Example 1 and obtained the exhaust gas purification catalyst of Example 3.

Example 4
Except for changing the blending amounts of iron nitrate nonahydrate and lanthanum nitrate hexahydrate to 1.25 parts by mass and 0.34 parts by mass, the same procedure as in Example 1 was performed, and LaFeO ₃ fine particles and iron oxide were added. 10 parts by mass of Nd—ZrO ₂ powder catalyst in which fine particles were co-supported (Fe ₂ O ₃ equivalent supported amount: 0.5 part by mass) was obtained.
Then, it carried out like Example 1 and obtained the exhaust gas purification catalyst of Example 4.

(Comparative Example 1)
Except for omitting the blending of lanthanum nitrate hexahydrate, the same procedure as in Example 1 was carried out, and 10 parts by mass of Nd—ZrO ₂ powder catalyst on which iron oxide fine particles were supported (Fe ₂ O ₃ equivalent supported amount: 0. 0). 5 parts by mass) was obtained.
Then, it carried out similarly to Example 1 and the exhaust gas purification catalyst of the comparative example 1 was obtained.

(Example 5)
As a base material particle, Y solid solution zirconia-based oxide (described as Y-ZrO ₂ , Y ₂ O ₃ : 35 mass%, ZrO ₂ : 65 mass%: D ₅₀ = 6.4 μm: BET specific surface area: 72 m ² / g) was used. 1.25 parts by mass of iron nitrate nonahydrate (containing 40% by mass in terms of Fe ₂ O ₃ ) and 0.9 part by mass of lanthanum nitrate hexahydrate (containing 75% by mass in terms of La ₂ O ₃ ) It melt | dissolved in 3.25 mass parts and prepared Fe and La containing aqueous solution. Impregnated with Fe and La-containing aqueous solution in the zirconia-based oxide, by 30min calcined at 600 ° C., LaFeO ₃ fine particles and iron oxide particles co supported Y-ZrO ₂ powder catalyst 10 parts by weight _(Fe 2 _{O 3} (Conversion carrying amount: 0.5 part by mass).
Thereafter, the obtained powder catalyst was subjected to a high temperature exposure treatment in an endurance furnace to obtain an exhaust gas purifying catalyst of Example 5. Note that as the high temperature exposure treatment, heat treatment was performed at 980 ° C. for 6 hours while sequentially switching the external atmosphere to A / F = 12.5, nitrogen atmosphere, and oxygen atmosphere.

(Comparative Example 2)
Except for omitting the blending of lanthanum nitrate hexahydrate, the same procedure as in Example 5 was carried out. As an exhaust gas purifying catalyst of Example 2, 10 parts by mass of Y-ZrO ₂ powder catalyst carrying iron oxide fine particles was supported. (Fe ₂ O ₃ conversion amount: 0.5 parts by mass) was obtained.
Then, it carried out similarly to Example 5 and the exhaust gas purification catalyst of the comparative example 2 was obtained.

<Powder X-ray diffraction measurement>
Using an X-ray diffractometer (trade name: X'Pert PRO MPD, manufactured by Yamato Kagaku Co., Ltd.), the obtained Y-ZrO ₂ powder catalyst supporting LaFeO ₃ fine particles and iron oxide fine particles was powdered under the following conditions. As a result of diffraction measurement, in Examples 1 to 5, the intrinsic peak of the LaFeO ₃ crystal was confirmed. FIG. 4 shows the X-ray diffraction pattern of Example 1.
Target: Cu
K-Alpha1 [A]: 1.5406
X-ray output setting: 40 mA, 45 kV
<Measurement of average crystallite size>
Further, when the average crystallite diameter was calculated based on the above formula (2), the average crystallite diameter of LaFeO ₃ of the exhaust gas purifying catalyst of Example ₃ was 19.4 nm, and the exhaust gas purifying catalyst of Example 5 was used. For the catalyst, it was 38.1 nm. The calculation by the Scherrer method was performed using commercially available software (Spectres, PANalytical X'Pert High Score Plus 3.0) based on a strong peak (002) near 32 °.

<EPMA elemental analysis>
Using an electronic probe microanalyzer (trade name: JXA-8100, manufactured by JEOL Ltd.), elemental analysis of the powder catalysts and exhaust gas purifying catalysts of Examples and Comparative Examples was performed under the following conditions.
<Conditions>
Electron gun Thermionic (LaB6)
Pretreatment Resin embedding (Specifix) -Wet polishing Conductive treatment Carbon deposition Acceleration voltage 15kV
Irradiation current 4.5 × 10 ⁻⁸ A
Step width 0.8μm
Number of steps 250 × 250
Measurement time 38msec
Probe diameter Focused
Measuring element [crystal]: Zr (Lα), Fe (Kα), Ce (Lα), Nd (Lβ), Pr (Lβ), La (Lα), Y (Lα)

  FIG. 5 shows the EPMA elemental analysis results of the powder catalyst and exhaust gas purification catalyst of Example 3, and the EPMA elemental analysis result of the exhaust gas purification catalyst of Comparative Example 1. FIG. 6 shows the EPMA elemental analysis results of the exhaust gas purifying catalysts of Example 5 and Comparative Example 2.

From the results of powder X-ray diffraction measurement and EPMA elemental analysis, it is confirmed that LaFeO ₃ fine particles and iron oxide fine particles are supported (attached) on the base material particles in the exhaust gas purifying catalysts of Examples 1 to 5. It was done. It can also be seen that in the exhaust gas purifying catalysts of Examples 1 to 5, the LaFeO ₃ fine particles and the iron oxide fine particles are uniformly and uniformly distributed in a highly dispersed state. On the other hand, in the exhaust gas purifying catalysts of Comparative Examples 1 and 2, it can be seen that the iron oxide fine particles are sintered and grown as a result of high temperature exposure. Therefore, in the exhaust gas purifying catalyst of the present invention having a structure in which LaFeO ₃ fine particles and iron oxide fine particles are co-supported on the base material particles, sintering and particle growth of the iron oxide fine particles during high temperature exposure are suppressed. It was confirmed that it was.

<Lab evaluation of running performance of exhaust gas purification catalyst>
In Examples 1 to 4 and Comparative Example 1, performance degradation (NO purification rate) due to high temperature exposure was evaluated. Here, in Examples 1 to 4 and Comparative Example 1, the NO purification rate before and after the high temperature exposure treatment is measured, and the NO purification rate after the high temperature exposure treatment is based on the NO purification rate (powder catalyst) before the high temperature exposure treatment. The deterioration rate was calculated. The measurement of the NO purification rate here was performed under the same conditions as the measurement of the NO purification rate of the powder particles described above. The evaluation results are shown in Table 1. In addition, in Table 1, it represented with the numerical value each normalized based on the NO purification rate of the powder catalyst of the comparative example 1 before high temperature exposure.

As is apparent from Table 1, the exhaust gas purifying catalyst of Comparative Example 1 carrying only iron oxide fine particles is excellent in NO purification performance immediately after the catalyst is produced, but the iron oxide fine particles are sintered by the high temperature exposure and grow. Therefore, it can be seen that the degree of deterioration is large, and as a result, the NO purification performance after high temperature exposure is poor. In contrast, the exhaust gas purifying catalysts of Examples 1 to 4 co-supporting LaFeO ₃ fine particles and iron oxide fine particles have a small degree of deterioration due to high temperature exposure, and have relatively large NO purification performance even after high temperature exposure. You can see that it is maintained. In particular, it has been found that the degree of deterioration due to high temperature exposure is particularly small when Fe: La is in the range of 4: 6 to 6: 4.

  INDUSTRIAL APPLICABILITY The present invention can be widely and effectively used as a three-way catalyst (TWC: Three Way Catalyst) for reducing NOx, CO, HC, etc. in exhaust gas, It can be used particularly effectively as a TWC for a direct catalytic converter in a tandem arrangement.

11 ... base particles 11a ... surface 21 ... LaFeO ₃ particles 31 ... iron oxide particles 100 ... exhaust gas purifying catalyst

Claims (11)

Base material particles containing a zirconia-based oxide;
LaFeO ₃ fine particles and iron oxide fine particles co-supported on the surface of the base material particles,
Exhaust gas purification catalyst characterized by containing at least. The content ratio of La and Fe is a molar ratio, and the following formula (1):
0.6 <Fe / La ≦ 1.6 (1)
The exhaust gas purifying catalyst according to claim 1, wherein: The exhaust gas purifying catalyst according to claim 1 or 2, wherein the LaFeO ₃ fine particles have an average crystallite diameter of 1 to 50 nm. The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the zirconia-based oxide is a rare earth element solid solution zirconia. The base material particles, the exhaust gas purifying catalyst according to claim 1 having an average particle diameter D ₅₀ of 3 to 30 .mu.m. A catalyst support;
The exhaust gas purifying catalyst according to any one of claims 1 to 5, which is held on at least a part of the catalyst carrier,
A catalytic converter for purifying exhaust gas, comprising: A step of applying an aqueous solution containing at least La ions and Fe ions to the surface of the base material particles containing a zirconia-based oxide; and the base material particles after the treatment are heat-treated at 500 to 1490 ° C. Co-supporting LaFeO ₃ fine particles and iron oxide fine particles on the surface of the material particles;
A method for producing an exhaust gas purifying catalyst, comprising: The content ratio of La and Fe in the aqueous solution is a molar ratio represented by the following formula (1):
0.6 <Fe / La ≦ 1.6 (1)
The manufacturing method of the catalyst for exhaust gas purification of Claim 7 which satisfy | fills. The method for producing an exhaust gas purifying catalyst according to claim 7 or 8, wherein the LaFeO ₃ fine particles have an average crystallite diameter of 1 to 50 nm. The method for producing an exhaust gas purifying catalyst according to any one of claims 7 to 9, wherein the zirconia-based oxide is a rare earth element solid solution zirconia. The base material particles, a method of producing an exhaust gas purifying catalyst according to any one of claims 7 to 10 having an average particle diameter D ₅₀ of 3 to 30 .mu.m.